Automatic turn-on and turn-off control for battery-powered headsets

ABSTRACT

Some workers wear headsets to protect their hearing from loud persistent noises, such as airplane engines and construction equipment. These headsets are generally passive or active, with the active ones including ear speakers and automatic noise-reduction (ANR) circuitry to cancel or suppress certain types of loud persistent noises. One problem with active headsets, particulary those that are battery-powered, concerns battery life. Workers often take the headset off or store them without turning them off and thus wasting costly battery life. Accordingly, the inventor devised active headsets with automatic turn-on and/or turn-off circuits. One exemplary embodiment senses a condition of the headsets, for example, the light, pressure, or temperature within one earcup, and then turns the headset on or off in response to the sensed condition.

CROSS-REFERENCE TO RELATED APPLICATION

[0001] This patent application is a continuation of U.S. provisionalpatent application 60/123,150 filed Mar. 5, 1999. This application isincorporated herein by reference.

TECHNICAL FIELD

[0002] The present invention concerns headphones or headsets,particularly battery-powered headsets with automatic noise-reductioncircuitry.

BACKGROUND OF THE INVENTION

[0003] Headsets typically include two earcups which are worn over earsof users to enhance or protect their hearing. For example, many workerswear headsets to protect their hearing from loud persistent noises, suchas airplane engines and construction equipment. These headsets aregenerally passive or active. Those that are passive only cover the earswith a sound-muffling material, whereas those that are active includeear speakers and automatic noise-reduction (ANR) circuitry. Thenoise-reduction circuitry automatically cancels or suppresses certaintypes of loud persistent noises. Active headsets are oftenbattery-powered and include an on-off switch to turn them on and off.

[0004] One problem with battery-powered headsets, particularly thosewith automatic noise-reduction circuitry, concerns battery life. Workershaving these headsets generally put on and take off their headphonesmany times throughout a workday, often forgetting to turn them off andwasting costly battery life. Moreover, for those headsets that are usedinfrequently with long storage times between uses, the turn-off problemis worse not only because their batteries are more apt to die, but freshbatteries are too often unavailable or inconvenient to obtain.

SUMMARY OF INVENTION

[0005] To address this and other needs, the inventor devised activeheadsets with automatic turn-on and/or turn-off circuits and relatedmode-control methods for active headsets. One exemplary embodimentsenses a condition of the headsets, for example, the light, pressure, ortemperature within one earcup, and then turns the headset on or off inresponse to sensed condition. Other embodiments that include automaticnoise-reduction (ANR) circuitry use an ANR driver to sense engagement ofan earcup with a user's head and an ANR microphone to sensedisengagement of the earcup from the user's head.

BRIEF DESCRIPTION OF THE DRAWINGS

[0006]FIG. 1 is a block diagram of a first exemplary headset 100incorporating the present invention.

[0007]FIG. 2 is a block diagram of a second exemplary headset 200incorporating the present invention.

[0008]FIG. 3 is a schematic diagram of an exemplary turn-on circuit 300incorporating the present invention.

[0009]FIG. 4 is a schematic diagram of an exemplary turn-off circuit 400incorporating the present invention.

[0010]FIG. 5 is a schematic diagram of an exemplary power-supply circuit500 for with turn-on circuit 300 and/or turn-on circuit 400.

[0011]FIG. 6 is a schematic diagram of an exemplary headset 600incorporating turn-off circuit 400 of FIG. 4.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0012] The following detailed description, which references andincorporates FIGS. 1-6, describes and illustrates one or more specificembodiments of the invention. These embodiments, offered not to limitbut only to exemplify and teach, are shown and described in sufficientdetail to enable those skilled in the art to implement or practice theinvention. Thus, where appropriate to avoid obscuring the invention, thedescription may omit certain information known to those of skill in theart.

[0013]FIG. 1 shows a first exemplary embodiment of an active,automatic-noise-reduction (ANR) headset 100 incorporating an automaticmode control feature in accord with the present invention. Headset 100includes an earcup 110 attached to a bridge member 112. Earcup 110 fitsover an ear and against the head of a user, represented generally assurface 111 in the Figure. (For simplicity, the figure omits a secondearcup.) Headset 100 also includes a mode sensor 120, and a mode-controlcircuit 130, an ANR sensor or microphone 140, ANR circuitry 150, and anANR driver 160. (ANR circuitry 150 includes one or more batteries and apower supply which are not shown.) (In some embodiments, the ANRfunction is implemented digitally.)

[0014] In operation, mode sensor 120, which is shown in broken form toemphasize that its placement can be virtually anywhere in or on theheadset, senses a condition of earcup 110 (or more generally headset100) and outputs a corresponding electrical signal to mode-controlcircuit 130. Mode-control circuit 130 processes the electrical signal,either switching the headset from a first operating mode to a secondoperating mode or leaving the headset in its current operating mode (orstate.) For example, if the signal indicates that the earcup has beendisengaged from the head of the user, mode-control circuit 130deactivates ANR circuitry 150 or otherwise puts it in a standby mode toreduce power consumption.

[0015] However, if the signal indicates that the earcup has been engagedwith the head of the user, mode-control circuit 120 enables or activatesANR circuitry 140 to control or otherwise affect the perceived acousticenergy within earcup 110. This generally entails ANR sensor 120outputting an electrical signal representative of acoustic energy withinearcup 110 to the ANR circuitry. In turn, the ANR circuitry processesthe electrical signal and outputs a responsive electrical signal to ANRdriver 140. ANR driver 140 ultimately produces an acoustic signalintended to cancel, suppress, or otherwise alter the acoustic energywithin earcup 110.

[0016] In some variants of this first embodiment, the sensor comprisesone or more mechanical switches, photo-sensors, temperature sensors, orpressure sensors. As used herein, light or photoelectric sensor includesany electrical or electromechanical device or component with usefulphoton-sensitive characteristics, coupled for use as a sensor.Temperature sensor includes any electrical device or component withuseful temperature-dependent characteristics, coupled for use as asensor. Pressure sensor includes any electrical or electromechanicaldevice or component with useful pressure-dependent characteristics,coupled for use as a sensor.

[0017] In some mechanical variants, a normally open or normally closedmechanical switch closes or opens on sufficient deflection of at least aportion of the earcup, such as an ear cushion, or deflection of a bridgebetween two earcups, upon engagement or disengagement of the headsetwith the head of the user (head surface or more generally user surface).Engagement or disengagement makes or breaks a normally open or normallyclosed electrical contact which in turn operates a switch (not shown)between a power supply and the ANR circuitry.

[0018] In some photo-sensing variants, the photo-sensors sense light ortemperature levels or changing light or temperature levels within orwithout the earcup. For photo sensors within the earcup or for photosensor on other interior (head-confronting) surfaces of the headset(such as a bridge between two earcups), engagement of the headsetgenerally reduces the sensed light and disengagement generally increasesthe sensed light.

[0019] Some temperature-sensing variants place the temperature sensorsthe head of the user, for example within the earcup on the bridgemember. Thus, the sensors generally see increases in temperature uponengagement of the headsets and decreases upon disengagement.

[0020] It is also contemplated that some photo-sensing ortemperature-sensing variants would facilitate automatically changingoperational modes as a user wearing a headset moves between indoor andoutdoor environments or between two indoor environments. For example,one can tune the sensors and/or mode control circuit to distinguishindoor environments from outdoor environments, correlate the distinctionto the intended use of the headset, and switch the headset on or off orotherwise change the acoustic control function of the headset.

[0021]FIG. 2 shows a second exemplary embodiment of an ANR headset 200including an automatic mode control feature in accord with theinvention. (FIG. 2 omits earcups for clarity.) Headset 200 includes anANR microphone 140, ANR circuitry 150, an ANR driver 160, and implementsautomatic mode control using a turn-off circuit 130 a, a turn-offcircuit 130 b, and a power switch 130 c. Turn-off circuit 130 a isresponsive to signals from ANR microphone 140 to control power switch130 c, and turn-on circuit 130 b is responsive to signals from ANRdriver 160 to control the power switch. Thus, unlike headset 100 in thefirst exemplary embodiment, headset 200 omits a dedicated mode sensor,and instead uses ANR driver 160 and microphone 130 as respective headsetengagement and headset disengagement sensors.

[0022] More specifically, engaging earcup 110 with the head of a usergenerally results in an appreciable mechanical deflection of ANR driver150, which responsively outputs an appreciable electrical signal toturn-on circuitry 130 a. If the signal exceeds a threshold, turn-oncircuitry 130 a activates power switch 130 c, thereby providing power toANR circuitry 150.

[0023] On the other hand, after engagement, the earcup and surface 111define a substantially closed volume that changes with user movements,such as head and jaw movements and the pulsating flow of blood throughthe confronting surface. In turn, these volume changes cause momentarypressure changes within the earcup, which are generally inaudiblelow-frequency events correlated only to engagement of the earcup withsurface 111. In response to these events, microphone 130 produces alow-frequency electrical signal which turn-off circuitry 130 b monitors.If the turn-off circuitry detects that this signal is absent for asufficient period of time, such as 2 or 3 or 5 or more minutes, itdeactivates power switch 130 c.

[0024]FIG. 3 shows details of an exemplary embodiment of turn-on circuit130 a. In this embodiment, the turn-on circuit includes a high-passfilter 310, a preamplifier 320, threshold detector 330, an inverter 340,a processor 350, a switch 360, power supply terminals V+ and Vgnd, and apositive battery terminal Vbattery+. V+ and Vgnd are respectively +2.5and zero volts in the exemplary embodiment. (Not shown in the diagramare one or more batteries, for example, AA batteries, and a switchingregulator which provides the voltages of +2.5 and −2.5 volts.) Inoperation, turn-on circuitry draws on the order of 10 microamps from oneor more supplied batteries. Hence, its impact on battery life isgenerally negligible.

[0025] More particularly, filter 310 comprises a 100-nanofarad capacitorC4 k and a resistor R6 k. Capacitor C4 k has first and second terminals,with the first terminal coupled to the output of the ANR circuitry, ormore precisely the ANR driver. The second terminal of capacitor C4 k iscoupled to ground via resistor R6 k and to the input of preamplifier320.

[0026] Preamplifier 320 comprises an LT1495 operational amplifier U1 a,a one-mega-ohm resistor R6 k, a 33 kilo-ohm resistor R7 k, a470-kilo-ohm resistor R15 a, and 100-kilo-ohm input resistor R16 a.Amplifier U1 a has a negative and positive inputs and an output. Thepositive input is coupled via resistor R16 a to a second terminal ofcapacitor C4 k, and the negative input is coupled to terminal Vgnd viaresistor R7 k. Resistor R6 k is coupled between the second terminal ofcapacitor C4 k and ground, and resistor R15 a is coupled between theoutput and the negative input of amplifier U1 a. The output of amplifierU1 a is coupled to the input of threshold detector 330.

[0027] Detector 340, which detects signals swings greater than 50millivolts, includes an LT1495 operational amplifier U1 b, a 1N914 diodeD1, and a one-mega-ohm resistor R8 k. Amplifier U1 b has a positiveinput coupled to the output of amplifier U1 a, and a negative inputcoupled to the positive terminal of diode D1. The negative terminal ofdiode D1 is coupled to ground, and resistor R8 k is coupled between thepositive terminal of diode D1 and positive supply terminal V+. Inverter166 has its input coupled to the output of amplifier U1 b, and itsoutput coupled to an input of processor 350,

[0028] Processor 350 responds to an output signal indicating engagementof the headset with the user by activating switch 360. Activating switch360, which in this embodiments comprises a p-channel mosfet transistor,connects power to the ANR circuitry enabling it to cancel or otherwisealter the acoustic energy within the earcup. A terminal of the mosfet iscoupled to a shutdown pin of integrated switching regulator.

[0029]FIG. 4 shows an exemplary embodiment of turn-off circuit 130 b.Turn-off circuit 130 b includes a microphone preamplifier 410, abandpass filter 420, a threshold detector 430, a processor 450, a switch460, respective positive and negative power-supply terminals V+ and V−,and a positive battery terminal (or node) Vbattery+. In the exemplaryembodiment, terminals V+ and V− respectively provide 2.5 and −2.5 volts.

[0030] In operation, ANR microphone 140 senses pressure within earcup120. When engaged with each other earcup 110 and surface 111 defines asubstantially closed space with a volume that changes with usermovements, such as head and jaw movements and the pulsating flow ofblood through surface 111. In turn, these volume changes cause momentarypressure changes within the earcup, which are generally inaudible,low-frequency events. On the other hand, when disengaged from surface111, earcup 110 is not pressed against surface 130 and thus no longerdefines a volume subject to user movements. Thus, microphone 140generally provides preamplifier 410 a signal with low-frequency contentthat changes during engagement of earcup 110 with surface 130 and thatremains relatively constant after disengagement.

[0031] More particularly, preamplifier 410 has a gain of 20 decibels andcomprises an input capacitor C10 a of 470 nanofarads, an input resistorR10 a of 470 kilo-ohms, an LMV324 operational amplifier U1 d, andfeedback resistors R12 a of 6.8 kilo-ohms and R14 a of 62 kilo-ohms.Amplifier U1 d provides an output signal proportional to the signal frompreamplifier 410 to band-pass filter 420. (In some embodiment,preamplifier 410 also functions as a portion of ANR circuitry 150 (shownin FIG. 2).

[0032] Band-pass filter 420, which defines a one-to-five hertz passbandwith an approximate gain of 30 decibels, comprises a resistor R1 k of330 kilo-ohms, a resistor R2 k of 330 kilo-ohms, a resistor R3 k of 33kilo-ohms, a resistor R4 k of 1 kilo-ohm, a resistor R5 k of 620kilo-ohms, and a resistor R1 m of 470 kilo-ohms. Filter 18 alsocomprises three 100-nanofarad capacitors C1 k, C2 k, and C3 k, and one470-nanofarad capacitor C1 m. Filter 180 also comprises an operationalamplifier U5 b which provides a pressure signal indicative of thepressure in earcup 120 via capacitor C1 m to threshold detector 430.

[0033] Threshold detector 430, which comprises an LMV324 operationalamplifier, a 470-kilo-ohm resistor R2 m, a 1-kiloohm resistor R3 m, anda 10-kilo-ohm resistor R4 m, compares the pressure signal to a225-millivolt reference voltage at a node C and outputs a signalindicating the result of the comparison to processor 440. When thepressure signal at node B is greater than the reference voltage at nodeC, detector 430 outputs a low signal, which indicates an “on-head”event, that is, engagement of earcup 110 with surface 110, to processor440.

[0034] In response to receiving an “on-head” event, processor 440 startsa timer which runs for a predetermined period of time, for example, twoto three minutes. If during this period, another “on-head” event doesnot occur, that is, there are no sensed low-frequency events ofsufficient magnitude, processor 440 assumes that the headset has beenremoved and sends an appropriate turn-off signal to a power-supplyshutdown circuit, which turns off the headset. In some embodiments,processor 440 directly drives a shut-down pin on a switching regulatorthat provides the V+ and V− supply voltages.

[0035]FIGS. 3 and 4 are shown as separate stand-alone circuits which areadaptable to virtually any active ANR headset to provide automatic modecontrol. When used together in the same headset, certain components ofthe circuits are shared to reduce the number of parts. For example, someembodiments use a single programmable processor and power switch.Moreover, some embodiments implement all or one or more portions of thecircuit as an integrated circuit.

[0036]FIG. 5 shows an exemplary embodiment of a power supply 500. Supply500 includes, among other things, battery connection terminals 510 a and510 b, one or more batteries 520, and a integrated switching regulatorcircuit 530. Regulator circuit 530 includes a shutdown pin, which in theexemplary embodiment, ultimately coupled to a terminal of switch 360 orswitch 460 in the turn-on and turn-off circuits of FIGS. 3 and 4. Thepresent invention is not limited to any particular power supplyarrangement.

[0037]FIG. 6 shows an exemplary embodiment of active headset 600including a turn-off circuit in accord with the invention. FIG. 6 alsoshows details of an exemplary ANR circuitry.

Conclusion

[0038] In furtherance of the art, the inventor has presented one or moreembodiments of active headsets incorporating an automatic mode controlfeature. One exemplary embodiment provides an turn-on and turn-offcircuits which automatically detect engagement and disengagement of aheadset to or from the head of a user to activate or deactivate theheadset. The turn-off circuit is especially useful to conserve batterylife in battery powered ANR headsets. However, the invention isgenerally applicable to automatically control the operational mode ofany active headsets or headphones, regardless of the power source.

[0039] The embodiments described above are intended only to illustrateand teach one or more ways of practicing or implementing the presentinvention, not to restrict its breadth or scope. The actual scope of theinvention, which encompasses all ways of practicing or implementing theconcepts of the invention, is defined by the following claims and theirequivalents.

1-8. (Canceled)
 9. An active headset having at least two operatingstates and comprising: one or more earcups; means for sensing acondition that is within at least one of the earcups; and means,responsive to a perceived absence of the condition, for changing theoperating state of the headset.
 10. The active headset of claim 9wherein the condition is inaudible.
 11. The active headset of claim 10wherein the means for sensing a condition within at least one of theearcups includes a microphone coupled to a bandpass filter, the bandpassfilter coupled to a threshold detector, the threshold detector coupledto a processor, and the processor coupled to a power switch.
 12. Theactive headset of claim 9 wherein one of the two operating states is anon state and the other is an off or standby state, and wherein the meansfor changing the operating state of the headset is responsive to thesensed condition to change from the on state to the off or standbystate.
 13. The active headset of claim 9 wherein the means for sensing acondition includes an audio transducer, light sensor, a pressure sensor,or a temperature sensor.
 14. The active headset of claim 9 wherein themeans for sensing a condition senses movement or acceleration.
 15. AnANR headset having at least two operating states and comprising: one ormore earcups; means for sensing a condition based on user jaw movementsor blood movement within a user's head; and means for changing theoperating state of the headset from an on state to an off state inresponse to a perceived absence of the condition.
 16. The headset ofclaim 15 wherein the predetermined period of time is at least oneminute.
 17. An ANR headset having at least two operating states andcomprising: one or more earcups; means for sensing a condition based onuser jaw movements or blood movement, wherein the means for sensingincludes a first audio transducer within one of the earcups; and means,coupled to the means for sensing the condition, for changing theoperating state of the headset from an on state to an off or standbystate, wherein the means for changing the operating state includes abandpass filter, a threshold detector, a processor, and a power switch,with the bandpass filter coupled between the threshold detector and thefirst audio transducer and the processor coupled between the thresholddetector and the power switch.
 18. The headset of claim 17, wherein themeans for changing the operating state of the headset changes theoperating state from the on state to the off state in response toperceived absence of the condition for at least one minute.
 19. Theheadset of claim 17 further including means for changing the operatingstate of the headset from the off state to the on state.
 20. The headsetof claim 17, wherein the one earcup engages the head of a user to definea volume and the means for sensing senses changes of the volume.
 21. AnANR headset having at least an active operating state and an inactive orstandby operating state and comprising: one or more earcups; an ANRmicrophone for sensing a condition based on user jaw movements or bloodmovement within the user's head; a timer circuit for measuring durationof a perceived absence of the condition; and a switch coupled to thetimer circuit for switching the ANR headset from one of the active andinactive operating states to the other of the active and inactiveoperating states.
 22. The ANR headset of claim 21, wherein the timercircuit comprises: a threshold detector; and a microprocessor coupled tothe threshold detector and to the switch.
 23. The ANR headset of claim21, wherein the predetermined amount of time is at least one minute. 24.A method of operating an ANR headset including an audio transducerattached to an earcup for engaging the ear of a user, the methodcomprising: sensing a condition; and switching at least a portion of theANR headset from an active state to an inactive or standby state inresponse to a perceived absence of the condition for at least apredetermined amount of time.
 25. The method of claim 24, whereinswitching at least the portion of the ANR headset comprises switching inresponse to sensing an absence of certain frequency content from theoutput of an audio transducer within the cavity for an amount of time ofat least one minute.
 26. The method of claim 24, wherein the ANR headsetincludes an ANR driver within the cavity and ANR circuitry coupled tothe ANR driver; and wherein the method further comprises switching theANR circuitry from the inactive state to the active state in response tosensing deflection of a portion of the ANR driver.
 27. The method ofclaim 24, wherein the certain frequency content is no greater than fiveHertz.
 28. The method of claim 27, wherein switching at least a portionof the ANR headset from an active state to an inactive state in responseto a perceived absence of the condition comprises: starting a timer inresponse to sensing the condition, with the timer configured to expireafter measuring the predetermined amount of time; and switching at leastthe portion of the ANR headset from the active state to the inactivestate in response to expiration of the timer.
 29. An ANR headsetcomprising: an input node for receiving an electrical signal correlatedwith a user wearing the headset; and a digital processor coupled to theinput node and configured to issue a turn-off command signal for atleast a portion of the ANR headset after perceiving an absence of theelectrical signal at the input node for at least a predetermined periodof time.
 30. The ANR headset of claim 29, wherein the electrical signalhas a frequency less than 5 Hertz.
 31. The ANR headset of claim 29,further comprising: circuitry, coupled to the input node, for detectingand indicating detection of a condition based on user jaw movements orblood movement.
 32. The ANR headset of claim 31, wherein the circuitryfor detecting and indicating detection of the condition, includes amicrophone, a bandpass filter, and a threshold detector, with thebandpass filter coupled between the threshold detector and themicrophone.
 33. The ANR headset of claim 29, further comprising a switchcoupled to receive the turn-off signal from the processor.
 34. The ANRheadset of claim 33, further comprising: a plurality of batteryconnection terminals for coupling to one or more batteries; and aswitching regulator circuit coupled to the plurality of batteryterminals, with the regulator circuit having a shutdown pin coupled to aterminal of the switch.
 35. An ANR headset comprising: at least oneaudio transducer for placement adjacent an ear of a user; circuitry forsensing a low-frequency electrical signal having a frequency no greaterthan five Hertz; and circuitry responsive to a perceived absence of thelow-frequency electrical signal to reduce power usage of the headset.36. The ANR headset of claim 35, wherein the circuitry for sensing alow-frequency electrical signal comprises: a bandpass filter; and athreshold detector coupled to the bandpass filter.
 37. The ANR headsetof claim 35, wherein the circuitry responsive to a perceived absence ofthe low-frequency electrical signal, to reduce power usage of theheadset, comprises: means, responsive to the perceived absence of thelow-frequency electrical signal, for reducing power usage of theheadset.
 38. The ANR headset of claim 35, wherein the circuitryresponsive to a perceived absence of the low-frequency electrical signalto reduce power usage of the headset, comprises: circuitry fordetermining whether the perceived absence has lasted at least apredetermined amount of time; and circuitry for reducing power suppliedfrom a power supply circuit to a portion of the ANR headset in responseto determining the perceived absence has lasted at least thepredetermined amount of time.
 39. The ANR headset of claim 38, whereinthe circuitry for reducing power supplied from the power supply circuit,comprises: a processor having an output pin; and a transistor coupled tothe output pin of the processor.
 40. The ANR headset of claim 38,wherein the predetermined period of time is at least one minute.